In recent years, a greenhouse effect resulting from an increase in carbon dioxide (CO2) concentration has been pointed out as a cause of global warming phenomena, and there is an urgent need to devise an international countermeasure to protect environment in a global scale. Industrial activities have a large responsibility as a generation source of CO2, and there is a trend to suppress discharge of CO2.
As technologies to suppress the increase of the concentration of acid gas, typically, CO2, there are a development of energy saving products, technologies to use the acid gas as a resource and to isolate and store the acid gas, a switching to alternate energies such as natural energy, atomic energy, and so on which do not discharge the acid gas, and so on, and a separation and recovery technology of discharged acid gas is known as one of them.
As separation technologies of the acid gas that have been studied up to now, there are an absorption process, a suction process, a membrane separation process, a cryogenic process, and so on. Among them, the absorption process is suitable for processing a large amount of gas, and its application in a factory and a power station is considered.
Mainly, as a method whose targets are facilities such as a thermal power station using fossil fuels (coal, coal oil, natural gas, and so on), a method in which exhaust combustion gas generated when the fossil fuel is burned is brought into contact with a chemical absorbent, and thereby CO2 in the exhaust combustion gas is removed and recovered, and further a method of storing the recovered CO2 are known. Further, there is proposed to remove acid gas such as hydrogen sulfide (H2S) in addition to CO2 by using the chemical absorbent.
In general, alkanolamine typified by monoethanolamine (MEA) have been developed in the 1930s as the chemical absorbent used in the absorption process, and are still used at present. A method of using the alkanolamine is economical, and further it is easy to enlarge the removal device in size.
As alkanolamine used in the absorption process, there are monoethanolamine, 2-amino-2-methylpropanol, methylaminoethanol, ethylaminoethanol, propylaminoethanol, diethanolamine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, triethanolamine, dimethylamino-1-methylethanol, and so on.
In particular, monoethanolamine being primary amine has been widely used because its reaction speed is fast. However, there are problems that this compound has corrosiveness, is easily deteriorated, and requires high energy for regeneration. On the other hand, methyldiethanolamine being tertiary amine has low corrosiveness and requires low energy for regeneration, but has a defect that an absorption speed is low. Accordingly, a development of a new absorbent in which these disadvantages are improved is required. Besides, an amine compound which is difficult to be released from an absorption tower and a regeneration tower is required.
In recent years, a study on particularly alkanolamine having structural steric hindrance, among amine compound, has been tried as the absorbent of acid gas. Alkanolamine having the steric hindrance has advantages that selectivity of acid gas is very high and the energy required for regeneration is small.
The reaction speed of the amine compound having the steric hindrance depends on the degree of reaction hindrance determined by the steric structure thereof.
There is a method to use the alkanolamine which has both the ether bond and the chained alkyl group which is directly coupled to a nitrogen atom.
However, the alkanolamine suffers from the disadvantages of the latively low boiling point, the insufficient suppression of the diffusion from the absorption tower, and high heat of reaction with acid gas.
On the other hand, there is a method to use a cyclic amine compound which has a chemical structure different from that of alkanolamine.